Interferons are a subclass of cytokines that exhibit both antiviral and antiproliferative activity. On the basis of biochemical and immunological properties, human interferons are grouped into three classes: interferon-alpha (leukocyte), interferon-beta (fibroblast) and interferon-gamma (immune). At least fourteen alpha interferons (grouped into subtypes A through H) having distinct amino acid sequences have been identified by isolating and sequencing DNA encoding these polypeptides. Alpha interferons have received considerable attention as potential therapeutic agents due to their antiviral and antitumor growth inhibition.
The purification of interferon from human leukocytes isolated from the buffy coat fraction of whole blood is described in U.S. Pat. No. 4,503,035. Human leukocyte interferon prepared in this manner contains a mixture of different human leukocyte interferon amino acid sequences. The purified material has a specific activity of from 0.9.times.10.sup.8 -4.times.10.sup.8 units/mg. of protein when assayed on the MDBK bovine cell line and from 2.times.10.sup.6 -7.6.times.10.sup.8 units/mg. of protein when assayed on the Ag 1732 human cell line.
The cytopathic effect inhibition assay used to determine interferon anti-vital activity is disclosed in U.S. Pat. No. 4,241,174. The measured interferon activity was calibrated against a reference standard for human leukocyte interferon provided by the National Institutes of Health.
The construction of recombinant DNA plasmids containing sequences encoding at least part of human leukocyte interferon and the expression in E. coli of a polypeptide having immunological or biological activity of human leukocyte interferon is disclosed in U.S. Pat. No. 4,530,901.
The construction of hybrid alpha-interferon genes containing combinations of different subtype sequences (e.g., A and D, A and B, and A and F) is disclosed in U.S. Pat. Nos. 4,414,150, 4,456,748, and 4,678,751.
U.S. Pat. Nos . 4,695,623 and 4,897,471 disclose novel human leukocyte interferon polypeptides having amino acid sequences which include common or predominant amino acids found at each position among naturally-occurring alpha interferon subtype polypeptides and are referred to as consensus human leukocyte interferon (IFN-con). The IFN-con amino acid sequences disclosed are designated IFN-con.sub.1, IFN-con.sub.2, and IFN-con.sub.3. The preparation of manufactured genes encoding IFN-con and the expression of said genes in E. Coli are also disclosed.
A purification of IFN-con.sub.1 produced in E. Coli is described in Klein et al. (J. Chromatog. 454, 205-215 (1988)). IFN--con.sub.1 purified in this manner is reported to have a specific activity of 3.times.10.sup.9 units/mg. protein as measured in the cytopathic effect inhibition assay using the T98G human cell line (Fish et al. J. Interferon Res. 4, 97-114 (1989)). Purified IFN-con.sub.1 comprises three isoforms as determined by isoelectric focusing which have been identified as methionyl IFN-con.sub.1, des-methionyl IFN-con.sub.1 and des-methionyl IFN--con.sub.1 with its N-terminus blocked by an acetyl group. (Klein et al. Arch. Biochem. Biophys. 276, 531-537 (1990)) .
Alpha-interferon is currently approved in the United States and other countries for the treatment of hairy cell leukemia, venereal warts, Kaposi's Sarcoma (a cancer commonly afflicting patients suffering from Acquired Immune Deficiency Syndrome (AIDS)), and chronic non-A, non--B hepatitis. Two variants of alpha interferon have received approval for therapeutic use: Interferon alfa-2a, marketed under the trade name Roferon.RTM.-A, and Interferon alfa-2b, marketed under the trade name INTRON.RTM. A. The amino acid sequences of Roferon.RTM.-A and INTRON.RTM. A differ at a single position but otherwise are identical to the amino acid sequence of alpha-interferon subtype 2 (subtype A).
In addition to the labeled indications, alpha-interferon is being used or evaluated alone or in conjunction with chemotherapeutic agents in a variety of other cellular proliferation disorders, including chronic myelogenous leukemia, multiple myeloma, superficial bladder cancer, skin cancers (basal cell carcinoma and malignant melanoma), renal cell carcinoma, ovarian cancer, low grade lymphocytic and cutaneous T cell lymphoma, and glioma. Alpha-interferon may be effective in combination with other chemotherapy agents for the treatment of solid tumors that arise from lung, colorectal and breast cancer (see Rosenberg et al. "Principles and Applications of Biologic Therapy" in Cancer: Principles and Practices of Oncology, 3rd ed., Devita et al . , eds . pp. 301-547 (1989) , Balmer DICP, Ann Pharmacother 24, 761-768 (1990)) .
Alpha-interferons are known to affect a variety of cellular functions, including DNA replication and RNA and protein synthesis, in both normal and abnormal cells. Thus, cytotoxic effects of interferon are not restricted to tumor or virus infected cells but are also manifested in normal, healthy cells as well. As a result, undesirable side effects arise during interferon therapy, particularly when high doses are required. Administration of interferon can lead to myelosuppression resulting in reduced red blood cell, white blood cell and platelet levels. Higher doses of interferon commonly give rise to flu-like symptoms (e.g., fever, fatigue, headaches and chills), gastrointestinal disorders (e.g., anorexia, nausea and diarrhea), dizziness and coughing. It would be useful to reduce or eliminate the undesirable side effects of interferon therapy without diminishing the therapeutic benefits of such therapy.
Therefore, an object of this invention is the treatment of conditions that are susceptible of treatment with an interferon, wherein the undesirable side effects normally associated with alpha interferon treatment are significantly diminished compared to currently practiced treatment regimens or eliminated entirely. Another object of the invention is to achieve enhanced therapeutic benefit in the treatment of diseases with interferon as compared to currently practiced regimens, with substantially no corresponding increase in the frequency or severity of undesirable side effects.